1. Field of the Invention
This invention relates to apparatus for fabricating a disk, such as a magnetic recording disk used in a computer hardfile, having surfaces textured by exposure to a pulsed laser, and, more particularly, to optical apparatus for determining profiles of texture features on such a disk by measuring scattered light reflected from the disk surface.
2. Background Information
Current hardfile drives use a Contact Start-Stop (CSS) system allowing a magnetic head, used to read and write data, to contact the surface of a magnetic disk in a specific CSS region when the disk is stationary. Thus, before the rotation of a spinning disk has stopped, the magnetic head is moved to the CSS region, where the magnetic head settles on the surface of the disk. When the disk again starts to rotate, the magnetic head slides along the disk surface in this region, until the laminar air flow at the disk surface, due to its rotation, fully lifts the magnetic head from the disk surface.
After the magnetic head is lifted in this way, it is moved from the CSS region to another region of the disk to read and write data. The CSS region is preferably textured to minimize physical contact between the magnetic head and the disk surface. In this way, the contact stick-slip phenomenon often called "stiction" and other frictional effects are minimized, along with the resulting wear of the magnetic head surface. Outside the CSS region the remainder of the disk surface preferably retains a specular smoothness to permit high-density magnetic data recording.
3. Description of the Prior Art
U.S. Pat. No. 5,062,021, to Ranjan et al., describes a process in which magnetic recording media are controllably textured, particularly over areas designated for contact with data transducing heads. In conjunction with rigid disk media, the process includes polishing an aluminum nickel-phosphorous substrate to a specular finish, then rotating the disk while directing pulsed laser energy over a limited portion of the radius, thus forming an annular head contact band while leaving the remainder of the surface specular. The band is formed of multiple individual laser spots, each with a center depression surrounded by a substantially circular raised rim. The depth of the depressions and the height of the rims are controlled primarily by laser power and firing pulse duration. The shape of individual laser spots can be altered by varying the laser beam inclination relative to the disk surface. On a larger scale, the frequency of firing the laser, in combination with disk rotational speed controls the pattern or arrangement of laser spots. The smooth, rounded contours of the depressions and surrounding rims, as compared to the acicular character of mechanical textured surfaces, is a primary factor contributing to substantially increased durability of laser textured media.
U.S. Pat. No. 5,539,213, to Meeks et al., describes an analyzing laser system which determines a physical characteristic of a repetitive texture pattern formed on a substrate surface. In one embodiment, the system used diffracted laser light to compute the average height of texturing bumps on a substrate surface. A laser beam is directed to the substrate surface and overlaps a group of individual marks or bumps formed in a repetitive pattern. A scanning linear photodetector array receives light diffracted from the surface. The digitized output of the array is the angular distribution of diffracted light intensities. In the preferred embodiment for determining the average height of laser-induced bumps formed on a specular magnetic recording disk substrate, the angular positions of the first and second diffraction peaks or rings are determined, and the intensities are integrated around these diffraction peaks or rings. These position and integrated intensity values are then compared to position and integrated intensity values for bumps of know height on calibration disk substrates. If the individual marks or bumps making up the repetitive pattern are also symmetrical, then the angular distribution of reflected light intensities is the square of the absolute value of the Fourier transform of the cross sectional profile of the bumps. Mathematical operations, including an inverse Fourier transform, are then performed on the digitized array output to yield the average cross sectional shape of the bumps illuminated by the analyzing laser.
What is needed is a method for examining the scattered light reflected from a textured surface in general, or a diffracted reflection of a laser beam from such a surface in particular without a need to perform complex calculations at a high speed.